Unpacking the IPCC Fifth Assessment Synthesis Report

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The Intergovernmental Panel on Climate Change (IPCC) is the most authoritative international body on climate science. The IPCC’s Assessment Reports provide a comprehensive summary of climate change, from the physical science to its impacts and how to tackle it. These reports inform our understanding of climate change and its implications for nations around the world, including Australia.

The IPCC’s latest report – the Fifth Assessment Report (AR5) – is the most comprehensive assessment of climate change undertaken. Ever. It involved thousands of contributing experts, including over 800 Lead Authors from more than 80 countries. AR5 is made up of four parts, each considering different aspects of the climate change challenge. On 2 November 2014 the fourth and final instalment of AR5 was released. Here is our summary of the four reports.

The Synthesis Report

Launched on 2 November 2014, the Synthesis Report integrates the assessment of past changes in climate as well as projections for the future from the three working group reports already released and two special reports brought out in 2011.

Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history.

The continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.

To provide a two-in-three chance or higher of keeping warming below 2°C will require limiting total CO2 emissions since 1870 to about 2900 gigatons. Two thirds of this amount had already been emitted by 2011. However, the remaining fossil carbon reserves (like coal, oil and gas) far exceed this remaining budget. The clear conclusion is that most fossil fuels have to stay in the ground.

By the end of the 21st century, it is very likely that more than 95% of the ocean area worldwide will experience sea level rise.

In urban areas, climate change is projected to increase risks for people, economies and ecosystems, including risks from heat stress, storms and extreme precipitation, inland and coastal flooding, water scarcity, sea-level rise, and storm surges.

Rural areas are expected to experience major impacts on water availability and supply, food security, infrastructure, and agricultural incomes.

In order to have any real chance of staying at or below 2°C, annual investments in low carbon electricity and energy efficiency will need to rise by several hundred billion dollars per year before 2030.

Without additional efforts to reduce emissions, global emissions growth will continue. If global emissions continue to rise on a "business as usual" basis global temperature will rise between 3.7 to 4.8 degrees C above preindustrial levels by 2100. This level of temperature increase would be catastrophic. That means we are heading towards catastrophic temperature rise.

We have the ability to tackle climate change and to build a more prosperous, sustainable future.

Our understanding of the climate system has continued to strengthen. Sea and air temperatures are rising, ice from glaciers and polar regions is being lost, and sea level is rising. For example, global average air temperature has risen by 0.85°C since the beginning of the 20th century.

Scientists are more certain than ever that increasing global temperature since 1950 has been caused primarily by rising emissions of greenhouse gases as a result of human activities. CO2 concentration in the atmosphere has increased by 40% since the beginning of the industrial revolution, primarily from the burning of fossil fuels.

A warming climate is increasing the frequency and severity of many extreme weather events and is changing rainfall patterns, creating risks for human well-being, the economy and the environment. For example, coastal flooding has increased since 1970, exacerbated by rising sea levels. If emissions continue to increase unabated average global sea level could rise by nearly 1 metre by 2100.

Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.

The second instalment of the IPCC’s Fifth Assessment Report is Climate Change 2014: Impacts, Adaptation and Vulnerability by Working Group II (WG II). It assesses the present understanding of how climate change will affect both human and natural systems and how these risks might be reduced and managed through adaptation and mitigation.

Key findings from the AR5 WG II report include:

There is now even more evidence that climate change presents serious risks to the world.

Species and ecosystems are already being significantly affected by climate change and this is projected to continue. For example, the Great Barrier Reef’s coral reef systems could be eliminated by mid-to late-century under current rates of ocean warming and acidification.

Climate change is having a negative impact on crop and agricultural food production. For example, marked decreases in water flows in the Murray-Darling Basin could occur if projections of severe dry conditions are realised.

Climate change has serious risks for human health. For example, an increased number of hot days is one of the most direct consequences of global warming and this can increase excess heat related deaths. Hot days in Melbourne, for example, are expected to increase by 20-40% by 2030.

The IPCC’s Summary for Policymakers provides an overview of the second report. We’ve also unpacked the second part of AR5 here and you can check out our video on the report too.

Working Group III

The third instalment of the IPCC’s Fifth Assessment Report is Climate Change 2014: Mitigation of Climate Changeby Working Group III (WG III). The mitigation of climate change involves reducing the sources of greenhouse gases. This WG III report considers all relevant options for mitigating climate change.

Key findings from the AR5 WG III report include:

CO2 emissions from fossil fuel combustion and industrial processes contributed to about 78% of the total greenhouse gas emission increase from 1970-2010, with a similar percentage contribution from 2000-2010. Decarbonising electricity generation is a key component of mitigation.

Mitigation scenarios that are likely to keep global temperature down to less than 2°C, relative to pre-industrial levels, include large-scale changes in energy systems and potentially land use.

In order to keep global CO2 levels to 450 ppm, the use of renewable energy will need to almost quadruple.

International cooperation is required to effectively mitigate greenhouse gas emissions.

The UN climate negotiations in Paris next year will bring countries together in an attempt to reach a binding and universal agreement on climate change. The findings of the IPCC’s Synthesis Report emphasises that now, more than ever, we need international action on climate change.

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